Github user andrewor14 commented on a diff in the pull request: https://github.com/apache/spark/pull/1165#discussion_r15242324 --- Diff: core/src/main/scala/org/apache/spark/CacheManager.scala --- @@ -140,14 +145,36 @@ private[spark] class CacheManager(blockManager: BlockManager) extends Logging { throw new BlockException(key, s"Block manager failed to return cached value for $key!") } } else { - /* This RDD is to be cached in memory. In this case we cannot pass the computed values + /* + * This RDD is to be cached in memory. In this case we cannot pass the computed values * to the BlockManager as an iterator and expect to read it back later. This is because - * we may end up dropping a partition from memory store before getting it back, e.g. - * when the entirety of the RDD does not fit in memory. */ - val elements = new ArrayBuffer[Any] - elements ++= values - updatedBlocks ++= blockManager.put(key, elements, storageLevel, tellMaster = true) - elements.iterator.asInstanceOf[Iterator[T]] + * we may end up dropping a partition from memory store before getting it back. + * + * In addition, we must be careful to not unroll the entire partition in memory at once. + * Otherwise, we may cause an OOM exception if the JVM does not have enough space for this + * single partition. Instead, we unroll the values cautiously, potentially aborting and + * dropping the partition to disk if applicable. + */ + blockManager.memoryStore.unrollSafely(key, values, updatedBlocks) match { + case Left(arr) => + // We have successfully unrolled the entire partition, so cache it in memory + updatedBlocks ++= + blockManager.putArray(key, arr, level, tellMaster = true, effectiveStorageLevel) + arr.iterator.asInstanceOf[Iterator[T]] + case Right(it) => + // There is not enough space to cache this partition in memory + logWarning(s"Not enough space to cache $key in memory! " + + s"Free memory is ${blockManager.memoryStore.freeMemory} bytes.") + var returnValues = it.asInstanceOf[Iterator[T]] --- End diff -- ok, though in the else case we can return `returnValues` directly
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